Traveling wave electron discharge devices



May 28, 1957 J. H. BRYANT 2,794,145

TRAVELING WAVE ELECTRON DISCHARGE DEVICES Filed Sept. 29, 1952 Z,APPROX. 0A 000 MULTIPLE [T- 0/? MULTIPLE lNVENTOR JOHN H. BRYANTATTORNEY United States Patent ice TRAVELING WAVE ELECTRON DISCHARGEDEVICES John H. Bryant, Nutley, N. L, assignor to InternationalTelephone and Telegraph Corporation, a corporation of MarylandApplication September 29, 1952, Serial No. 312,155 Claims. (Cl. 315-35)This invention relates to traveling wave electron discharge devices andmore particularly to transducer or transition arrangements for matchinga low impedance radio frequency line tothe relatively high impedancehelical line usually employed in such devices.

In my joint copending application with T. J. Marchese, Serial No.221,862, filed April 19, 1951, for Traveling Wave Electron DischargeDevice, an impedance matching transformer is disclosed comprising ashort section of an axially disposed coaxial line of high impedance, thesame as that of the helical line to which the inner conductor iscoupled. The opposite end of the coaxial section is shorted to establisha voltage null point. The radio frequency coaxial line of lowerimpedance is coupled to the coaxial section of high impedanceintermediate the ends thereof at a point presenting the proper impedancematch. While such a coaxial transition section makes a good impedancematch it requires valuable coaxial space thus limiting the length of thehelix and, therefore, the gain.

One of the objects of the present invention, therefore, is to provide animpedance matching transition at the end of the helical line whichrequires a minimum of axial space thereby making it possible to have alonger helix for a tube or device of given size.

One of the features of the invention is the placing of the transitionsection transversely of the axis of the helical line. This feature isaccomplished by providing a parallel line arrangement preferablyutilizing a conductive plate, which serves as an alignment plate forelements of the device disclosed in the aforesaid copending application,as one of the conductors. By providing a second conductor insubstantially parallel spaced relation to the planar surface of theplate, a transmission line is provided which will propagate radiofrequency energy in the TEM mode. By making this transition section ofsuch a length as to be resonant at the operating frequency of the tubeand by shorting one end thereof to establish a standing wave having avoltage null point at the shorted end and a voltage max point adjacentthe helical line, it is a simple matter to couple the low impedancecoaxial line to the transition section at an appropriate point betweenthe voltage null and max points thus obtaining a proper impedance match.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent by reference tothe following description taken in conjunction with the accompanyingdrawings, wherein:

Fig. 1 is a fragmentary view in longitudinal section with parts of theenvelope broken away of a traveling wave electron discharge deviceincorporating transition sections at the ends of the helical line inaccordance with the principles of this invention;

Fig. 2 is a view in elevation of the transition section as viewed alongline 22 of Fig. 1;

Fig. 3 is a cross-sectional view similar to Fig. I of anotherembodiment, as viewed along line 3-i3 of Fig. 4;

2,794,145 Patented May 28, 1957 Fig. 4 is an elevational view of thetransition arrangement illustrated in Fig. 3 and as viewed along line4-4 thereof;

Fig. 5 is an elevational view similar to Figs. 2 and 4 of still anotherembodiment of the invention;

Fig. 6 is a view in cross-section taken along 6-6 of Fig. 5;

Fig. 7 is a view in cross-section similar to Fig. 6 showing stillanother embodiment of the invention; and

Fig. 8 is a view in elevation of the transition section shown in Fig. 7as viewed along line 8-8 of Fig. 7.

Referring to Figs. 1 and 2 of the drawings, the traveling wave electrondischarge device or tube therein shown follow generally the constructiondisclosed in the aforementioned copending application, modified toincorporate one form of the transition sections of the presentinvention. The device comprises a cathode 1, focusing elec trode 2 andan anode electrode 3 for the emission and forming of electrons into abeam for flow lengthwise of the tube. The three electrodes are mountedas a gun unit and supported on an alignment or partition plate 4received in position within a metal cylinder 5 against an abutment 6formed on the inner surface thereof. At the rear of the tube anotheralignment or partition plate 7 is provided which likewise is receivedwithin cylinder 5 against an abutment 8. The alignment plate 7 normallysupports the R. F. terminal section particularly the R. F. outputterminal and, in certain embodiments, may also support the R. F. inputterminal. Supported between the two alignment plates 4 and 7 is ahelical line 9 which serves to propagate the radio frequency energy fromthe input terminal line 10 to the output terminal line 11 by way oftransition sections 12 and 13. The helical line 9 is preferablysupported by dielectric rods 14, 15 and 16 which are disposed at spacedpoints about the helix and extend parallel to the axis of the helix.These rods 14, 15 and 16 are in turn supported at their ends in openingscontained in conductors 17 and 18 of the transition sections, asindicated in Fig. 2. Centrally of these openings, which accommodate thesupporting rods, is an opening 19 which receives the end of the helix,which in this embodiment is connected to the conductor 17. It will beunderstood, however, that the opening 19 may be considerably smallerthan that shown, and in fact, may correspond to the inner diameter ofthe helix. It should also be understood that the rods may be of anysuitable dielectric material such as glass, ceramics or quartz, and ifdesired, the rods may be replaced by a tube of such material.

While all of the details of the traveling wave electron discharge devicehave not been shown in Fig. 1, it will be understood that sulficientstructure is included to illustrate the principles of the presentinvention. For example, the magnetic field established parallel to theaxis of the helix may be established by either a permanent magnet orsolenoid 20. In this connection the alignment plates 4 and 7 arepreferably chosen of magnetic material so as to assist in establishingthe paths of magnetic flux for axial concentration of the magneticfield. It will also be noted that the plate 7 provides a support for thecollector electrode 21 disposed-axially of the helix. For additionaldetails of the tube structure reference may be had to the aforesaidcopending application Serial No. 221,862.

The transition sections of the present invention'employ the plates ofthe alignment structure as a part thereof. As shown in Figs. 1 and 2,the forward transition section comprises the plate 4 and the conductor17. The conductor 17 is-maintained in proper spaced relation withrespect to the planar surface of the plate 4 to present the proper lineimpedance. In this embodiment both ends of the conductor 17 are shortedto the plate 4, as indicated at 22 and 23. The length of the conductor17 is chosen approximately one-half wavelength or a multiple thereof ofthe Operating frequency so as to establish a resonant section havingnull voltage points at the shorted ends thereof and a maximum voltagepoint or zone adjacent the end of the helix 9. The input, terminal lineis in the form of a coaxial line, the outer conductor 24 of which isreceived in an opening contained in the plate 4 to which the conductor24 is connected, and the inner conductor is connected to the conductor17 as indicated at 26. The R. F. energy conducted over the terminalconnection 10 is propagated along the transition section in the TEM modeand is thereby coupled for propagation along the helical line 9 whileone conductor of the transition section is here shown to be thealignment plate 4, it will be understood of course, that it may be aseparate strip conductor if desired.

As previously pointed out, the coaxial line 10 has a relativelylowcharacteristic impedance which for example may be in the order of 50ohms, while the helical line 9 has a relatively high characteristicimpedance, for example 300' ohms or more. The transition section 12provides for proper matching of the terminal connection It by couplingthe coaxial terminal 10 at a suitable point 26 between the voltage nullpoint at 22 and the voltage max point at 19. Likewise, the coupling ofthe helical line at the voltage max point of the transition section 12insures a proper impedance match therebetween.

The transition section 13 at the output end of the helical line is, inthis embodiment identical, to the section 12, the transition sectionbeing coupled to the output coaxial terminal line 11 at a proper pointfor impedance matching. In each transition section it will be readilyapparent that a minimum amount of axial space is utilized within thedevice for effecting the transition coupling between the coaxialterminals and the helical line. While the transition sections are shownto be at right angles to the axis of the helical line, it will beapparent that the sections need not be at right angles but may be variedtherefrom depending on the structure of the device and the supportingarrangement of the alignment plates. It should also be understood thatwhile I have shown the transition section as employing an alignment orpartition plate a separate planar conductor may be provided.

Referring to Figs. 3 and 4 another embodiment of the invention is shown,wherein the strip conductor 17:: of the transition section is madeconsiderably narrower than the strip 17 of Figs. 1 and 2. The strip 17afor example, may comprise round stock in cross-section, although othercross-sectional configurations, such as rectangular, triangular andelliptical, may be employed. In this form the strip 17a is offset fromthe opening 27 contained in the plate 4a so that the strip is disposedadjacent to the path of the electron beam which flows through theopening 27. The helical line 99a is coupled to the strip 17a and isprovided with a suitable support similarly as hereinbefore described tomaintain the helix in axial align ment with the opening 27. The coaxialterminal connection 10a is made to the transition line conductors 4a and17a similarly as described in connection with Figs. 1 and 2.

While the conductor strips 17 and 17a shown in Figs. 1 to 4 areconnected at both their ends to the associated plate conductor, theyneed not be so arranged. For example, in Fig. l the upper portion of thetransition strip 17 above the helical line 9 may be omitted, therebyproviding, in effect, an open ended transition section of approximatelyone-quarter wavelength. Such a transition section is shown in Figs. 5, 6and 7, 8. In this embodiment the transition section 28 is shown tocomprise in addition to the planar plate conductor 4b a narrower stripconductor 29. The narrow strip 29 may be round, triangular, rectangular,oval or other cross-sectional configuration, as may be desired, and asshown is approximately. one-quarter wavelength long. In order toproperly support the voltage max end 30 of the strip 29 with respect tothe planar surface of the plate 4b additional strips 31 all) and 32 aredisposed at right angles to the strip 29 and connected to or otherwisemade integral with the end 30 thereof. The outer ends of the strips 31and 32 are in turn connected to the plate 4b, approximately one-quarterwavelength from the point 30 thereby presenting a rigid three-armedstructure. The point 30 is disposed adjacent the end of the helical linefor coupling the R. F. energy between coaxial terminal 10b and thehelical line.

While the strip conductors of the transition sections in Figs. 1 to 6are shown supported in spaced relation to the planar surface of anassociated plate conductor by means of metallic connections associatedwith both ends of the strip conductor this is not essential Where thestrip is sufliciently strong to be self-supporting from the shorted endas shown in Figs. 7 and 8. In this embodiment the conductor material ofthe strip 33 is of suflicient width and thickness as to be supported atone end to the plate 40 with the remainder in substantially parallelrelation to the surface of the plate 4c. The high voltage open end iscoupled to the helical line 9c adjacent the beam path 34. The coaxialterminal connection is coupled to the transition section at the properimpedance matching point between the voltage null and max points of thesection.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made by way of example only and not as a limitationto the scope of my invention, as set forth in the objects thereof and inthe accompanying claims.

I claim:

1. In a traveling wave electron discharge device having a radiofrequency coaxial line, a helical line and means to provide a beam ofelectrons for flow along a path axially of said helical line; aconductor in the form of a plate disposed between said, helical line andsaid beam providing means in transverse relation to said beam path, saidplate conductor having an opening therethrough in alignment with theaxis of said beam path, a second conductor having a length resonant atthe operating frequency at said discharge device disposed in parallelspaced relation for substantially the entire length thereof to thesurface of said plate conductor, said second conductor having one endthereof connected to said plate conductor at a given point spaced fromsaid opening to establish at said one end a voltage null point and ahigh voltage point adjacent said opening for coupling radio frequencyenergy to said helical line, means coupling the outer conductor of saidcoaxial line to said plate conductor and means coupling the innerconductor of said coaxial line to said second conductor intermedate saidhigh voltage point and said voltage null point to obtain an impedancematch between said helical line and said coaxial line.

2. In a traveling electron discharge device having a radio frequencycoaxial line, a helical line and means to provide a :beam of electronsfor flow along a path axially of said helical line; a conductor in theform of a plate disposed between said helical line and said beamproviding means, said plate conductor having an opening therethrough inalignment with the axis of said beam path, a second conductor disposedin parallel spaced relation for substantially the entire length thereofto the surface of said plate conductor, said second conductor having onepart connected to said plate to establish a voltage null point andanother part disposed adjacent said opening and at a distance from saidnull point to establish a high voltage point adjacent said opening forcoupling radio frequency energy to said helical line, and means couplingthe outer conductor of said coaxial line to said plate conductor and theinner conductor to said second conductor, both ends of said secondconductor being connected to said plate conductor, the length of saidsecond conductor being equal substantially to one half a wavelength oran odd multiple thereof of the operati-ng frequency of said device.

3. In a traveling electron discharge device having a radio frequencycoaxial line, a helical line and means to provide a beam of electronsfor flow along a path axially of said helical line; a conductor in theform of a plate disposed between said helical line and said beamproviding means, said plate conductor having an opening therethrough inalignment with the axis of said beam path, a second conductor disposedin parallel spaced relation for substantially the entire length thereofto the surface of said plate conductor, said second conductor having onepart connected to said plate to establish a voltage null point andanother part disposed adjacent said opening and at a distance from saidnull point to establish a high voltage point adjacent said opening forcoupling radio frequency energy to said helical line, and means couplingthe outer conductor of said coaxial line to said plate conductor and theinner conductor to said second conductor, said second conductor beingprovided with support extensions extending laterally thereof adjacentthe high voltage point, said lateral extensions being disposed in spacedrelation to said plate conductor with the outer ends thereof connectedto said plate conductor, the length of said lateral extensions beingequal substantially to one quarter wavelength or an odd multiple thereofof the operating frequency of said device.

4. In a traveling electron discharge device having a radio frequencycoaxial line, a helical line and means to provide a beam of electronsfor flow along a path axially of said helical line; a conductor in theform of a plate disposed between said helical line andsaid beamproviding means, said plate conductor having an opening therethrough inalignment with the axis of said beam path, a second conductor disposedin parallel spaced relation for substantially the entire length thereofto the surface of said plate conductor, said second conductor having onepart connected to said plate to establish a voltage null point andanother part disposed adjacent said opening and at a distance from saidnull point to establish a high voltage point adjacent said opening forcoupling radio frequency energy to said helical line, and means couplingthe outer conductor of said coaxial line to said plate conductor and theinner conductor to said second conductor, said second conductorcomprising a flat strip with one side disposed in spaced substantiallyparallel relation to a planar surface of said plate conductor, the partof said strip adjacent said opening being connected to the conductor ofsaid helical line.

5. In a traveling electron discharge device having a radio frequencycoaxial line, a helical line and means to provide a beam of electronsfor flow along a path axially of said helical line; a conductor in theform of a plate disposed between said helical line and said beamproviding means, said plate conductor having an opening therethrough inalignment with the axis of said beam path, a second conductor disposedin parallel spaced relation for substantially the entire length thereofto the surface of said plate conductor, said second conductor having onepart connected to said plate to establish a voltage null point andanother part disposed adjacent said opening and at a distance from saidnull point to establish a high voltage point adjacent said opening forcoupling radio frequency energy to said helical line, and means couplingthe outer conductor of said coaxial line to said plate conductor and theinner conductor to said second conductor, said second conductorcomprising a flat strip with one side disposed in spaced substantiallyparallel relation to a planar surface of said plate conductor, saidstrip having both ends thereof connected to said plate conductor, thelength thereof being equal substantially to onehalf a wavelength or anodd multiple thereof of the operating frequency of said device, and anopening therethrough in alignment with the axis of said beam path, aportion of said strip adjacent said last mentioned opening beingconnected to the conductor of said helical line.

References Cited in the file of this patent UNITED STATES PATENTS2,403,290 Korman July 2, 1946 2,432,057 Wheeler Dec. 2, 1947 2,516,944Barnett Aug. 1,.1950 2,575,383 Field Nov. 20, 1951 2,578,434 LindenbladDec. 11, 1951 2,584,802 Hansell Feb. 5, 1952 2,637,775 Lund May 5, 1953OTHER REFERENCES Article by Kompfner, pages 124-127, Proc. 1. 1g. E.,for February 1947.

